Lithium secondary batteries are widely used as power sources for communication and information equipments such as cell phones, notebooks, and digital cameras due to their high operating voltage, improved charge-discharge cycle, and their adaptability to miniaturization. In addition, the anticipated large-scale commercialization of an electric car is expected to a rapidly increasing demand for the lithium secondary batteries.
LiCoO2, which is easily synthesized, and has such desired characteristics as high reversibility, low self-discharge rate, high capacity, and high energy density, had been generally used as a cathode active material of lithium secondary batteries. However, for the purpose of reducing the amount of high-priced Co used, lithium salts containing equivalent amounts of Co, Ni and Mn, i.e., three element-based lithium metal oxides are currently used as the cathode active material. An aluminum foil with a lithium salt-containing coating layer formed thereon is used as a cathode, the coating layer being formed using a mixture of the lithium salt, a binder and a solvent.
Besides Co, Ni, Mn, and Li are also valuable, relatively expensive metals, and there have been active studies on economically feasible methods for recovering such metals. These metals are generally recovered by treating the wastes (composition comprising valuable metals such as Co, Ni, Mn, and Li, impurities such as Al, Fe, and Cu, and carbon; hereinafter, referred to as “scrap powders”) with an inorganic acid; removing impurities from the resulting leaching solution; and extracting each of the valuable metals present in the resulting leaching solution with an appropriate organic solvent to selectively isolate each metal component.
For example, Korean Patent Publication No. 2009-87801 discloses methods of improving the leaching rates of metals to be recovered by using a various highly concentrated acids at the leaching process. Such conventional methods, however, have the problem that as excessive amounts of acids are present in the leaching solution, the use of a large amount of an expensive neutralizing agent is required in the purifying and solvent-extraction processes.